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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 12 May 2016 by John Cook

It’s been almost a month since the paper I co-authored on the synthesis of research into the scientific consensus on climate change was published. Surveying the many studies into scientific agreement, we found that more than 90% of climate scientists agree that humans are causing global warming.

My co-authors and I even participated in an Ask Me Anything (AMA) session on the online forum Reddit, answering questions about the scientific consensus.

While my own research indicates that explaining the scientific consensus isn’t that effective with those who reject climate science, it does have a positive effect for people who are open to scientific evidence.

Among this “undecided majority”, there was clearly much interest with the session generating 154,000 page views and our AMA briefly featuring on the Reddit homepage (where it was potentially viewed by 14 million people).

Here is an edited selection of some of the questions posed by Reddit readers and our answers.

Q: Why is this idea of consensus so important in climate science? Science isn’t democracy or consensus, the standard of truth is experiment.

If this were actually true, wouldn’t every experiment have to reestablish every single piece of knowledge from first principles before moving on to something new? That’s obviously not how science actually functions.

Consensus functions as a scaffolding allowing us to continue to build knowledge by addressing things that are actually unknown.

Q: Does that 97% all agree to what degree humans are causing global warming?

Different studies use different definitions. Some use the phrase “humans are causing global warming” which carries the implication that humans are a dominant contributor to global warming. Others are more explicit, specifying that humans are causing most global warming.

Within some of our own research, several definitions are used for the simple reason that different papers endorse the consensus in different ways. Some are specific about quantifying the percentage of human contribution, others just say “humans are causing climate change” without specific quantification.

We found that no matter which definition you used, you always found an overwhelming scientific consensus.

Q: It’s very difficult to become/remain a well-respected climate scientist if you don’t believe in human-caused climate change. Your papers don’t get published, you don’t get funding, and you eventually move on to another career. The result being that experts either become part of the 97% consensus, or they cease to be experts.

Ask for evidence for this claim and enjoy the silence (since they won’t have any).

As a scientist, the pressure actually is mostly reversed: you get rewarded if you prove an established idea wrong.

I’ve heard from contrarian scientists that they don’t have any trouble getting published and getting funded, but of course that also is only anecdotal evidence.

You can’t really disprove this thesis, since it has shades of conspiratorial thinking to it, but the bottom line is there’s no evidence for it and the regular scientific pressure is to be adversarial and critical towards other people’s ideas, not to just repeat what the others are saying.

Q: What’s the general reasoning of the other 3%?

Interesting question. It is important and diagnostic that there is no coherent theme among the reasoning of the other 3%. Some say “there is no warming”, others blame the sun, cosmic rays or the oceans.

Those opinions are typically mutually contradictory or incoherent: Stephan Lewandowsky has written elsewhere about a few of the contradictions.

Q: Do we have any insight on what non-climate scientists have to say about climate change being caused by CO2?

In a paper published last year, Stuart Carlton and colleagues surveyed biophysical scientists across many disciplines at major research universities in the US.

They found that about 92% of the scientists believed in anthropogenic climate change and about 89% of respondents disagreed with the statement: “Climate change is independent of CO2 levels”. In other words, about 89% of respondents felt that climate change is affected by CO2.

Q: It could be argued that climate scientists may be predisposed to seeing climate change as more serious, because they want more funding. What’s your perspective on that?

Any climate scientist who could convincingly argue that climate change is not a threat would:

be famous

get a Nobel prize

plus a squintillion dollars in funding

a dinner date with the Queen

lifelong gratitude of billions of people.

So if there is any incentive, it’s for a scientist to show that climate change is not a threat.

Q: I was discussing politics with my boss the other day, and when I got to the topic of global warming he got angry, said it’s all bullshit, and that the climate of the planet has been changing for millennia. Where should I go to best understand all of the facts?

But often facts are not enough, especially when people are angry and emotional. The Skeptical Science team has made a free online course that addresses both the facts and the psychology of climate denial.

Comments

I tell people that Scientific consensus is important less for Scientists, and more for Policymakers. And in lay discussions, the Policy is actually what is being discussed. The 'Do Nothing' alternative is promoted on the basis that the Science isn't 'proven' or 'complete' (which is an odd thing to promote, since logically an 'incomplete Science' should call us to 'Do twice as much of Something' if we were true conservatives). But if Policymakers admit that they aren't Scientists, then Scientific Consensus is the justification for action. On this topic, Policymakers of the last 30 years have taken the 'Do Nothing' alternative based on a 'whopping' 3-10% consensus of expert opinion. It's hard not to conclude they simply ignored the Scientists and made policy on the basis of intuition. We shall see how that goes.

It is ironical that this discussion is misleading as it is the operation of technical systems that have contibuted to climate disruption and ocean acidification and warming. Human have only made the decisions that led to these unintended consequences of the technical systems using fossil fuels.

The current level of CO2 is 400 parts per million which means there is one cubic foot of CO2 for every 2500 cubic feet of air. What is the measure of how much temperature rise is caused by this amount of CO2?

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Moderator Response:

[PS] You might like to look at the myths "CO2 is just a trace gas" and "CO2 only causes 35% of warming". You might like to clarify your question. I assume you mean how much of the temperature rise since pre-Industrial is caused by increase of CO2 since then. With 0% CO2 in atmosphere, earth would be frigid ice ball. Do you mean how much temperature rise by direct radiative effect, or how much by radiative plus feedbacks? (decreased albedo, increased water vapour etc).

What I'm asking is what method has been used to measure CO2's contribution to global temperature rise?

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Moderator Response:

[PS] See here for direct measurement. See "There is no empirical evidence" for other papers measuring the effect. (Harries, Wang, Evans, Philipona, Grigg, Chen all on that page). The IPCC chapter on "Attribution" covers methods for working out contribution in excruciating detail.

The referenced papers, in my opinion, do not prove that the increase in radiative forcing has been sufficient to have any measureable effect on temperature change as recorded since 1880. The fact that atmospheric CO2 rise has been constant but temperature rise has not been continuous does not support a finding that CO2 levels are influencing temperature.

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Moderator Response:

[PS] These papers show that energy radiating to earth surface increase precisely in line with predictions. Unless you want to revoke Plancks Law and conservation of energy, this must increase temperature. To discuss correlation with temperature, please see the myth "There is correlation with temperature". Please note that nowhere does science claim a linear correlation with temperature - CO2 is not the only factor in surface temperature, especially on scales less than a couple of decade. This site is not the place for rhetorical tricks like strawman arguments.

You might find the "Arguments" item on the top menu bar helpful for finding resources about your apparent beliefs. Please read the article carefully before commenting and if you want to dispute the science, please ensure that you have understood what the science claims first, not taking some misinformation site's word for it.

Your "fact" that temperature rise has not been continuous even though CO2 rise has been "constant" would only be a reasonable conclusion if CO2 was the only thing that affected global temperatures. It is not, and there are lots of posts on this site that will educate you if you bother to look. Although many factors affect short-term trends (and some longer-term), the current rise in temperatures cannot be explained by those other factors and it is entirely consistent with the known physics of CO2 and radiation transfer.

Your logic is like saying that your long-term increase in your bank balance is not caused by your regular paycheck because the bank balance drops sometimes (when you pay bills) - even though you have no other source of income.

I still have seen no proof that the current level of atmospheric CO2 has any measureable effect on temperature readings. The fact that an entity has the quality of causing something does not guarantee that it will cause that something if there is not enough of the entity. For example, steel has the quality of being able to stop the flight of a bullet. A thickness of one inch of steel will stop a bullet fired from a pistol but 1/2500th of an inch of steel won't. The recorded temperature change the Earth has been experiencing since 1880 conforms to the statements by climatologists that a 500 year period of warming began about 1850 with the end of the of a 500 year period of cooling that had begun around 1350. This would not appear to have anything to do with atmospheric CO2 levels, Also, I think that continuous recording of the pattern of heat loss that occurs between the Earth's surface and the temperature recording devices would be key to determining whether changes in the atmosphere were acting upon that heat loss and to what extent.

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Moderator Response:

[PS] I am quite sure that if you do not want to accept GHG theory, then nothing will change you mind. However, if you can show an example of increased irradiation of a surface not increasing its temperature, then line up for a Nobel prize. Furthermore you seem to postualating that the earth can warm or cool without a cause (ie a violation of 1st law). Please cite the "the statements by climatologists" - otherwise this is sloganneering and prohibited. Since most of the earth is covered by ocean, most of heat goes there. How to explain this energy build up with your "natural cycles"?

I am not postulating that the Earth can warm or cool without cause. What that cause is I do not know but I would tend to think it is an alteration in the Earth's relationship with the Sun. I also think that if one wishes to prove that carbon dioxide in the atmosphere is the cause of global warming then the focus of temperature measurement should be upon those few feet between the Earth's surface and the measuring instruments employed on land for measuring that temperature. The nature of the heat loss from the earth's surface to those instruments might reveal whether it is a linear loss or whether it is influenced by an outside agent such as carbon dioxide in the atmosphere. As far as increased irradiation not increasing surface temperature, this could occur if the irradiation was so small that its effect could not be measured with the instrumentation available.

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Moderator Response:

[PS] Orbital forcings are directly calculated. Their influence is well studied (maybe start here). How you accept that this forcing, slow and very small compared to GHG, affected climate and yet GHG do not. To suggest that GHG affect thermometers 2m about surface is to profoundly misunderstand how GHG effect works. I suggest you go to the basics. How about the ocean measurements then?

Proof that CO2 causes temperature change. Perhaps rephrase that. Proof that CO2 influences the planets energy balance, and that in turn changes in the energy balance then change temperatures.

The earths energy balance is heat flowing in from the Sun and heat flowing out to space. If those two flows don't match, the amount of energy here on Earth can change. If heat in is greater than heat out, heat here on Earth builds up. And the size of these energy flows is staggering. A rate of around 121,500 trillion watts in and out. AN energy flow in of that magnitude, if it wasn't balanced by a flow outwards, is enough energy to boil the oceans dry in less than a 1000 years. Even a small imbalance in these flows can cause significant changes.

So something that can influence the flow of energy out to space, restricting it in some way, would have a profound impact.

The following graph is from a paper published in 1970. It is measuring the energy flowing out to space from a point on the Earth below, from near Galveston in Texas. To understand the graph, think of it like a rainbow. It is plotting the energy flowing to space for a range of different wavelengths in the infrared region, infrared 'colours' if you like. So the amount of energy flowing out to space is proportional to the area under the curve.

There are to curves. One is a calculation from theory, the other was a direct measurement, taken by the Nimbus 3 satellite in 1969, the first time this sort of measurement could be taken from space. Today such measurements are everyday occurances. One graph has been shifted up for clarity, actually the two graphs match almost perfectly, such was the state of this science in 1969.

Remembering that the energy flowing to space is proportional to the area under the graph, look at the big notch. That is less energy reaching space than would be expected. That is a disruption of the outward heat flow that sets the Earth's energy balance. And that is caused by CO2. There is the Greenhouse Effect and the impact of CO2 all in one observation.

The Earth is over 30 degrees warmer than it otherwise would be because of it.

00

Moderator Response:

[PS] Billev seems to accept that photons received direct from sun will affect temperature, but that photons coming from gases in the atmosphere somehow magically do not affect temperature (or energy balance). If someone is willing to deny something has experimentally tested and fundamental as Plancks Law, then I doubt any science will convince them.

If the CO2 caused energy imbalance is the reason for the Earth's temperature rise then that temperature rise should be continuous like the steady, and accelerating, rise of CO2 in the atmosphere. But the record of the Earth's mean temperature since 1880 shows that the rise in the Earth's temperature has not been continuous. There have been two thirty year periods of no temperature increase that have alternated with two thirty year periods of temperature rise. Why this inconsistency?

00

Moderator Response:

[TD] Read the post "CO2 Is Not the Only Driver of Climate." Put further comments on that thread, not this one, for this topic in this comment of yours. Further off-topic comments by you will be deleted without warning, because you have had plenty of warnings.

[GT] billev, I have replied to your comment on the thread TD linked to.

Back on topic, there is a clear issue about if a consensus has any place in scientific process? The question was asked, "wouldn’t every experiment have to reestablish every single piece of knowledge from first principles before moving on to something new?" Point being the justification to rely on a consensu.

Although it is true scientific papers do NOT reestablish every piece of knowledge, when writing and publishing journal articles, we certainly do reference prior work to support the arguments and experimentation going forward. It is improper to begin a scientific journal article as "everyone believes X" and therefore, we move on to the next hypothesis, experimentation and conclusion. The "everyone believes" is not science.

A properly written scientific article, using Global Warming as an example, would be like the following and part of the Abstract/Introduction section of a scientific journl article.

"Current global warming theory dictates that CO2 has been a major driver of climate change throughout the 20th century (Ref, ref, ref, ref, ref). A variety of studies demonstrate CO2 forcing has a direct impact to global mean temperatures (ref, ref, ref, ref, ref)....."

There is no need to invoke a consensus, the prior body of scientific literature supports the new paper. There is no need to reestablish all prior knowledge, you just properly reference it.

joeygoze @13, I have yet to see a scientific paper reference Newton's laws of dynamics, or of optics, or the laws of thermodynamics (except, for the later, for those written in the very early 20th century or earlier). Even such recently developed theories as plate tectonics are not referenced in papers discussing issues centrally related to it (eg, orogeny). In similar manner, it would be astonishing to find a modern climate science paper referencing that CO2 is a major driver of climate, or that changes in CO2 concentration have a direct impact on global mean surface temperatures unless the paper was from an entirely different field (where assumption of such basic knowledge cannot be made), or where the reference is not for the fact of influence, but for a specific estimate of the value of the impact.

The reason for such lack of referencing is that these are examples of 'text book knowledge', ie, facts that are so well established in the field that it can be reasonably supposed that anybody in the field (or for Newton's laws of dynamics and optics, any scientist) will know them, and have an approximate idea of their origin. They are also facts which are simply accepted as a matter of course - about which there is a consensus.

In general, specific referencing indicates that the fact in question is either controversial within the field, or specialist knowledge which is probably only known to a very few members of a sub-discipline. In the example of orogeny, things which are probably well known to specialists in Chinese orogony, but not to experts in orogony in general, let alone all geologists are referenced. Consensus, as measured by a lack of need to reference, trails the real consensus among experts because textbooks trail current knowledge - but it is real, and is relied on in science, for if scientists had to reference everything they would never get anything done.